Lids for closing containers used for storing food products usually include a pre-fractured line which facilitates opening of the container.
The pre-fracture line is made on lids which have already been painted, so the pre-fracturing operation might cause cracks and/or breaks in the covering paint.
The lids therefore require a further stage of painting in order to cover the exposed points.
Document EP 0.971.051 describes an apparatus for performing repainting on lids, by immersing them in an electrophoretic bath.
The apparatus described in this document comprises a tank containing an electrophoretic bath, an electrode, for example a negative-polarity electrode (cathode), immersed in the bath, a conveyor line bearing support elements for the lids to convey them in immersion internally of the bath in the tank, and a contact unit, for example having positive polarity (anode), to establish an electrical contact with the lids during transit thereof immersed in the bath, which contact unit is positioned above the tank.
The contact of the lids immersed in the bath with the anode contact unit determines passage of the current from the negative electrode (cathode), via the electrophoretic bath, to the lids themselves: in consequence of this passage of current, the solid particles present in the bath adhere to the lid, mainly in the exposed points, and coat them.
The contact unit for realizing an electrical contact with the lids, for example with a negative polarity (anodic unit), used in the apparatus described in EP 0.971.051, is very complex.
It comprises a chain element arranged ring-wound with an operative tract that extends parallel above the tract of the conveyor line along which the lids are immersed in the bath.
The chain element is provided with support blocks, made of a non-conductive material, to which small tongues are fastened, made of a conductive material, such as to be positioned transversally to the chain element.
The tongues are destined to make contact with the lids transiting immersed internally of the bath of the tank.
In this respect, each tongue comprises a first end for contacting the lids, and a second end for contacting an electrically positively-polarized bar, positioned parallel to the operative tract of the chain element.
The chain element must be activated such that the tongues, which run along the operative tract which extends above the conveyor line, first contact (with their first end) the transiting lids immersed in the bath, and consequently contact, with their second ends, the positively-polarized bar, in order to obtain anodic contact with the lids, when they are still immersed in the bath.
The above-described anodic unit exhibits a complex structure, and the cleaning operations of the single tongues are not particularly easy and also require the apparatus to be stopped.
Further, maintenance in the case of breakage of one or more tongues requires a considerable inoperative time.
The aim of the present invention is therefore to provide an apparatus for electrophoretic repainting of metal objects, in particular lids for containers for food use, which can realize an electrical contact with the lids immersed in the electrophoretic bath in a way which is both simple and immediate.
A further aim of the invention is to provide an apparatus for electrophoretic repainting of lids for containers of food products, which enables the contact units, which contact the lids, to be cleaned without having to stop the apparatus from operating.
A further aim of the invention is to provide an apparatus for electrophoretic repainting of lids which is provided with a unit for electrical contact with the immersed lids, which has a simple and functional structure in realization of the contact with the lids immersed in the electrophoretic bath.